Method and apparatus for smelting fine iron ore



June 12, 1956 Filed Jan. 4, 1952 W. E. MARSHALL METHOD AND APPARATUS FORSMELTING FINE IRON ORE 2 Sheets-Sheet l ATTORN 8Y3.

June 12, 1956 w, MARSHALL 2,750,276

METHOD AND APPARATUS FOR SMELTING FINE IRON ORE Filed Jan. 4, 1952 2Sheets-Sheet 2 llllll INVENTOR.

#41 4 MM lT/Zmasmu QM fallow ATTORNEYS.

United States PatentC METHOD AND APPARATUS FOR SMELTING FINE IRON OREWilliam E. Marshall, Middletown, Ohio, assignor to Armco SteelCorporation, Middletown, Ohio, a corporation of Ohio Application January4, 1952, Serial No. 264,859

15 Claims. (CI. 75-26) It has long been known that finely divided ironore could be converted to a mixture of metallic iron and gangue bytreating it at an elevated temperature with suitable reducing gases. Theend product of such a procedure, however, has not been readilyutilizable. If it is to be used directly, it involves a seriousseparation problem, and the finely divided iron must be melted down formost uses. It is possible to feed the finely divided mixture of iron andgangue into a blast furnace or the like where the usual iron smeltingprocedure is being carried on. Melting will effect a separation of theiron from the gangue; but any economies theoretically derivable from thepre-reduction of the iron are largely lost in such a procedure.

In a copending application Serial No. 226,231, filed May 14, 1951, andentitled Process and Apparatus for Reducing and Smelting Iron, I havedescribed a procedure and apparatus in which a flame is produced in abath-type furnace from a mobile fuel, the flame having a temperature ofat least substantially 3000 F., and the products of combustion of theflame being reducing to iron oxide. The heat from the flame is employedto maintain a bath of iron'in molten condition in the bath-type furnace,and the products of combustion of the flame, which are reducing incharacter, are employed outside the bath-type furnace proper to reducefinely divided iron ore, the iron and the ganguebeing then melted insidethe furnace by the heat of the flame. The conditions required for thepractice of this process, and in particularthe production of a flamewhich has a sufiiciently high temperature and nevertheless is reducingtoward iron, may be met' by the use of oxygen or oxygen-enriched air forpurposes of combustion and by a preheating of the mobile fuel or theoxygen or oxygen-enriched air or both. In that application and in thepresent case, the'terrn mobile fuel isused to mean natural andartificial combustible gases, such as natural gas, methane, ethane,propane, butane, ethylene,.

acetylene, hydrogen and the like, which contain as their principalcombustion components hydrogen or hydrocarbons, (but without more than'a minor'concentration of gases containing combined oxygen, suchascarbon monoxide and water vapor), as wellas. to mean oil: or otherliquid hydrocarbon fuels, and solid, pulverized, carbonaceous fuels,such as powdered coal, coke, or carbon black. The process is capable ofeffecting substantial economies especially where a plentiful supply of amobilefuel is economically obtainable. Since the iron. ore is used in afinely divided condition, a cheaper iron ore may be employed; and theuse of lump coke as a skeleton in a shaft furnace or asa fuel isavoided.

One of the principal objects'of this invention is the provision ofimprovements in the process and apparatus of the said copendingapplication.

Another object is the provision of means and a methodwhich willfacilitate the obtaining of a high: temperature flame from burningfuelwhile maintaining the reducing character of:the-products of combustionthereof.

Yet another object, of one aspect ofxthe invention, is.

the provision of means and amethodof accomplishing, the

Patented June 12, 1956 ICC smelting of iron by meansof mobilefuels inwhich the iron molten bath. of iron and slagis being maintained by the,flame.

Yet'another object of the invention is the provision of means and amethod. for the' more economical and complete utilization of the: heat.generated in the process. Specifically, but without limitation, when itbecomes necessary to cool the reducing products of combustion from thefurnace in order toutilize them in reducing iron ore, I employ theheat-absorbed from: these gases in the production of the requiredtemperatures at the'point of combustion.

Yet another object of the invention is the provision of a process andapparatus for accomplishing the general object of the said copendingapplication, but ina simpler, less expensive, and-more positiveway.

These and other objects of the invention, which will be set forthhereinafter or will be apparent to one skilled in the art upon readingthese specifications, I accomplish by that procedure and in thatapparatus, of which I shall now describe certain exemplary embodiments.Reference is made to the accompanying drawings in which:

Figure 1 is a diagrammatic showing in the nature of a flow-sheet, ofapparatus appropriate to the practice of my invention.

Figure 2 is a similar showing of a modified form of apparatus.

Referring to Figure 1, I have shown therein a bath-type furnace,indicated generally at 1, having a hearth 2 upon which a bath of iron 3and a supernatant bath of slag 4 are maintained in molten condition bythe heat of a flame 5 produced by a burner 6. The products of combustionof the flame enter a chamber 7 of the furnace which is arranged as aheat exchange apparatus. As shown, this chamber contains a conduit 8 incoiled or sinuous condition or otherwise arranged so as to effectuate anefiicient heat transfer. A suitable mobile fuel, such for example, asnatural gas, is introduced into the conduit 8 from a suitable source bymeans of the conduit 9 shown outside the furnace. The mobile fuel,without being exposed to or commingled with the products of combustionof the. flame 5 is thus subjected to a high'temperature such thatcracking occurs therein, the fuel separating principally into itscomponents, carbon and hydrogen.

The cracked or partially cracked mobile fuel leaves the heat exchangemeans 8 through a conduit 10. Additional cracking or heating meansv maybe employed, as in the stove 11, equipped with an interior sinuousconduit 12. The stove 11' may be heated by the combustion of a portionof the gases from the furnace 1 (which, being reducing in nature,contains combustible values), or by the combustion of fuel derived fromany other source. To. this end .I have shown the stove 11 equipped witha burner 13 havingan inlet 14 for fuel and an inlet 1'5'for air.

The. cracked and heated gases from the stove 1-1 are conducted by aconduit 16. to the burner 6 of the furnace 1. In theburner they aremixed with. oxygen or oxygenenriched air (preheated if desired) enteringthe burner through a conduit 17 An intense flame within the furnace 1 isthus produced, while. the products of cornbustion of the flame remainreducing in character.

in my process-the cracking of the mobile fuel absorbs heat and requiresabout 20% to' 30% of the total heat used in the process; As aconsequence, applying this heat to the mobile fuel, using for thepurpose either the sensible heat from the gases. of furnace 1 or theheat of combustion of waste-gas=or othenextrinsicifuel, makes theprocess more efficient, and increases the:..rate. of production ofmolten iron. Further, since in some embodiments of my process thereducing gases from the products of combustion of the furnace 1 areemployed outside the furnace to reduce iron ore and must be cooled forthis purpose from the high temperature of the furnace to a tempera tureof around l300-l400 F. or slightly higher, it will be seen that theportion of my apparatus thus far de scribed offers a mode oftransferring heat usefully and directly to gases entering the burner 6.The cracking temperature for most mobile fuels will be around 1600 F.,so that it will be seen that this arrangement affords a means forwithdrawing suflicient heat from the furnace gases to crack the mobilefuel and at the same time reducing the temperature of the furnace gasesto a range at which efiicient reduction of iron ore will occur outsidethe furnace without causing such sintering of the reduced iron as wouldclog pipes, conduits and chambers in which the reduction is carried on,or in which the reduced or partially reduced iron ore is being carried.

A cracked mobile fuel, at temperatures around the cracking point, is, initself, an eflicient reducer for iron ore, and may be employed directlyfor such reduction, the reduced or partially reduced iron and ganguebeing introduced into the furnace 1 through the burner 6 along with thefuel and oxygen or enriched air. To this end I have shown in Figure 1 ameans for the introduction into the conduit 9 of finely divided iron oreand a finely divided flux such as lime. These means havediagrammatically been illustrated as comprising a hopper 18 for the ironore and flux, and a screw feed means 19 driven by a motor 2% forproducing a uniform rate of feed into the conduit 9. The velocity of thegases passing through the conduit and the associated heat exchangeddevices and conduits will be sufficiently great to carry the iron oreand flux suspended therein. Indeed, I may also introduce into theincoming mobile fuel stream any reduced iron ore and flux derived fromreduction apparatus, using the products of combustion of Figure 1,located outside the furnace l. I have shown such materials being alsointroduced into the conduit 9 through a conduit 21. The various finelydivided materials introduced into the stream of mobile fuel and passingtherewith through the cracking apparatus not only are subjected toreducing conditions, but serve also two primary functions. They catalyzethe cracking of the mobile fuel, and they also act as scouring means tokeep such apparatus free from an accumulation of carbon which mightotherwise clog them, the carbon, of course, being derived from thecracking of the mobile fuel.

In a procedure in which all of the iron ore which is to be reduced inthe process is introduced as such into the stream of fuel, thecombustion gases from furnace 1 may be burned elsewhere for the usefulgeneration of heat, or may in part be purified and used to dilute theincoming fuel. But it is more economical to use the reducing values ofthe gases from furnace 1 for pre-reducing iron ore, the reduced productbeing then introduced into the furnace along with the cracked fuel ashereinabove described, or in any of the direct modes of introductiondescribed in my copending application Serial No. 226,231. The furnacegases from furnace 1, which have now been cooled in the heat exchangeapparatus 7, 8 as hereinabove described, may be carried by a conduit 22to a preheater and partial reductionchamber 23. A finely divided mixtureof iron ore and flux, such as lime, may be introduced into the conduit22 so as to be carried along by the gas stream therein. Introductionapparatus is diagrammatically shown as comprising a hopper 24, a screwfeed means 25 and an electric motor 26. It will be understood that otherfeeding means may be substituted. It will also be understood that anymixture of iron ore and flux which is introduced into my apparatus willbe in sufi'iciently dry condition to prevent plugging the system or thegeneration of such a concentration of water vapor as would interferewith the reduction of the iron values in the ore.

The reduction chamber 23 is preferably of that type in which the finelydivided materials, i. e. the iron ore and flux are maintained fluidizedor in a condition of con tinuous agitation by reason of the flow ofincoming gases through the conduit 22. The finely divided materialsaccumulate in the chamber 23' until they spill over the partition 27therein, entering a downtake 28 and accumulating above a valve 29connected with a conduit 3d. The material collecting above valves 2) and32 will be in at least partially reduced condition. The action of reduc--tion, which in part involves the combination of hydrogen in the gaseswith the oxygen of the iron ore, serves to produce a concentration ofwater vapor in the gases which impairs their reducing efficiency inspite of the fact that they still otherwise contain substantial reducingvalues. As a consequence, I carry these gases through a dust separator31 of the centrifugal or other type and through conduit 33 to a gasdehydrator 34 where the moisture-vapor content. is largely removed.Solids from the dust separator 31 collect above a valve 32, and aredelivered to the conduit 3%.

A pump 35 is used to move the gases. The reducing capacity of the gasesis now to a large extent restored; but the gases have been so lowered intemperature that it becomes necessary to reheat them to the range atwhich efficient reduction of iron ore will occur. This may beaccomplished by means of the stove 36, the gases passing through asinuous conduit or heat exchange means 37 within the stove. The stovemay be fired by waste gases derived from the system or by fuel from someother source; and I. have shown a burner 33 equipped with an inlet 39for fuel and an inlet 40 for air.

The hot, dry gases, which are now again reducing toward iron, arecarried by a conduit 41 to the entrance end of conduit 30 into which areintroduced, as above described, the solids from the first reductionstep. These solids are entrained in the reducing gases in the conduitand are carried thereby to a second reducing chamber 42 which, again,preferably is of the fluidizing type. The reduced material accumulatesin the downtake 43 of this chamber while the gases are carried to a dustseparator 44. Solids separated by this device are carried by a branchconnection to the downtake 43 where they accumulate above a valve 45.This valve connects the downtake to the conduit 21 by means of which thereduced solids are carried to the intake conduit 9 for the mobile fuel,as hereinabove described.

The gases from the dust separator 44 have relatively low reducingefliciency, but contain substantial combustible values. Hence, they arecarried by a conduit 46 to a gas holder or accumulator 47 where they maybe stored for use. It will be understood that the gases so held may bethe combustible gases used for heat in the stoves 11 and 36 and thatexcess quantities of them may be employed for other purposes, such asthe drying of the ore and flux for introduction into separators 18 and24, the production of oxygen for use in the burner 6, or for theenrichment of the air used in that burner, for the generation of power,or for any other uses of a combustible gas.

Referring now to Figure 2, like parts have been given like indexnumerals and will not be again described. The mobile fuel for the burner6 is shown as being cracked in the stove 11, entering the heat exchangeapparatus within that stove through a conduit 48. In this particularembodiment of my apparatus, the upper part of the furnace 1 is used fora different purpose hereinafter described. It is not beyond the scope ofmy invention, however, to use some portion of the sensible heat of theproducts of combustion of furnace 1 to preheat the mobile fuel and crackit at least in part. The cracking may be accomplished with or withoutthe introduction of iron oreand flux and/ or partially or completelyreduced iron and gangue into the mobile fuel, as will readily be under-5. stood from the description of; Figure? 1-, although in Figure 2 Ihave not shown means for this purpose.-

The furnace 1* has an upper chamber 49 connected with the main part of:the furnace by a relatively constricted: throat 50. In this embodimentof my invention,'I- carry on a reduction of the iron ore. in the chamber-49-directly by means of the reducing gaseswhi'ch are the products ofcombustion of the flame 5.

Finely divided iron ore' and flux are. introduced into the chamber 49,as from a hopper-51, by means of a screw feed 52 equipped witha motor53. The purpose of the constriction 50- is to increase the velocity ofthe products of combustion-passingfrom the furnace properinto thechamber 49 so as to maintain the finely divided solids in a state ofsuspension in the chamber-49; The: velocity of the gases may be still.further increased by the introduction through the conduit 54' ofadditional quantities of reducing gas preferably derived-from the stackgases as hereinafter described, or' of fresh' reducing gas: such asnatural gas or the like.

It will be-underst'ood that" the reduction in the chamber 49 will betaking place at a very high temperature; It has been described abovethat the temperature of the flame in the bath-type furnace 1 might be:of the order of about 3000 F. or higher in order-to maintainthe iron andslag in suitably molten condition- The temperatures, therefore, in thechamber 49 will be lower than about 3000 F. only by the amount ofcooling which has occurred during the passage of the gases tothe chamber49 and the amount of cooling by dilution which has occurred through theintroduction of reducing gases through the conduit 54. The temperaturesin therchamber -49', therefore, will be high enough to produce sintering'or' coalescence of the reduced materials. Nodulization will occur, butonly after the reduction: is substantially complete. When heavy enoughnodules are formed'so-"that the gases'at their specific velocity canno-longer keep-them in'suspension, they will fall through therthroat50=intothe main part of the furnace and be melted into the sla'grandiron baths 4 and 3.

While as indicated above, unreduced iron ore and flux may be fed intothe chamber 49 and there reduced as described, the process is moreefiicient if a pre-reduction of the iron ore is practiced. Thisreduction need not necessarily be a complete reduction and in mostinstances will not be so. But the furnace 1 will deliver largequantities of products of combustion which are high in reducing values,and these reducing values will by no means be entirely absorbed orconverted in the chamber 49. Consequently, I prefer to deliver the gasesfrom this chamber through a conduit 55, a dust separator 56 and aconduit 57 to the dehydrator 34. The same type of pump 35 may beemployed to move the gases; and if the gases are cooled, as when thedehydration is accomplished by cooling with cold water, it will benecessary to reheat the gases in the stove 36 hereinabove described.

The dehydrated and hot reducing gases are delivered by a conduit 58 to aconduit 59 into which a mixture of dry, finely divided ore and flux suchas lime, is delivered, as by means of the hopper 24, screw 25, and motor26. These solids are entrained in the hot reducing gases and carried toa reducing chamber 60 such as the chambers 23 and 42 previouslydescribed. The reduced solids enter the downtake 61 of this reducingchamber, while the gases from the reducing chamber go to a dustseparator 62. The solids from this separator are carried by a branchconnection 63 to the same downtake, as are also the solids from the dustseparator 56, by a downtake 64. These solids accumulate above a valve 65by means of which they are delivered to the hopper 51. It will be clearthat the downtake 61 is connected to the hopper by a gas-tightconnection, in this embodiment of my process, so that the reducedmaterials are not re-exposed to the atmosphere.

The gases from the dust separator 62, which are now relatively low in.reducing valuesalthough they: containv example, cokefor increasing:the-carbon content-.of thev iron. or alloying ingredients-for the directproduction of alloy steels-.-v

Modifications maybe made in my invention without departing fromthespirit. of. it. In particular, the various. 1' individual featuresof. any apparatus described herein may be combined in various ways.Having; thus described my invention. in' certain exemplary embodiments,

what I claim as new-and desire to secure by Letters- Patent isa.

1. Ina: process of? reducing and. smelting iron ore including the stepsof "producing-in a furnacewitha mobile'fuel-a flame-having a temperatureof at least substantially 3000 F., the products of combustion-of whichare reducing to iron oX-ide, employing said reducingproducts-"ofcombustion in-heated condition to reducefinelydivided: iron ore toiron,iand melting said. reduced iron. by means of the heatv of saidfiame,-thefurther steps. of -cracking; said mobilev fuel-priortoignition thereof to produce said flame by the application of heat tosaid mobile-fuel; and. having present in said fuel at the time ofcraekingtafinely divided material which 'is introducedr-into.saidfurnace. through said flame.

2. The process claimedvin claim 1 wherein the said finely divided.material comprises. iron-bearing material entrained in saidmobile fuel.

3. A process of reducing and smelting iron ore which comprises producingin a furnace with a mobile fuel a flame having a temperature of at leastsubstantially 3000' F., the products" of combustion of which arereduc'ingft'o iron oxide, employing a portion of the sensible heat ofsaid 'products' of combustion to crack said mobile fuel at 'l'east-inpart prior to the ignition thereof to produce said flame, employing saidreducing products of combustion in heated condition to reduce dividediron ore to iron and melting said reduced iron in said furnace,including the step of entraining finely divided material in said fuelprior to the cracking thereof.

4. The process claimed in claim 3, wherein finely divided iron-bearingmaterial is entrained in said mobile fuel prior to the cracking thereof,and wherein said finely divided iron-bearing material is introduced intosaid furnace along with said fuel.

5. A process of reducing and smelting iron which comprises producing ina furnace with a mobile fuel a fiame having a temperature of at leastsubstantially 3000 F., the products of combustion of which are reducingto iron oxide, said furnace having upper and lower chambers, passingsaid products of combustion into said upper chamber at a velocitysufiicient to maintain finely divided iron-bearing material insuspension therein, and feeding finely divided iron-bearing materialinto said upper chamber, the temperature of said products of combustionbeing sufficient to bring about agglomeration of particles of saidiron-bearing material when at least partially reduced, wherebyagglomerates of said particles attain a weight too great to be supportedby said products of combustion, whereupon said agglomerates pass bygravity from said upper chamber and are melted in said lower chamber.

6. The process claimed in claim 5, wherein the velocity of said productsof combustion is increased by the introduction into said furnace ofreducing gas at a point remote from the origin of said flame.

7. The process claimed in claim 6, wherein the products of combustionafter passing through said upper chamber are dried and employed toreduce iron ore at least in part, the reduced material being thenintroduced in particulate form into said upper chamber.

8. The process claimed in claim 7, in which said mobile fuel is crackedprior to the ignition thereof to form said flame, and has entrainedtherein finely divided ironbearing material during said cracking.

9. In apparatus for the purpose described, a sealed furnace having ahearth chamber and an upper chamber, said upper chamber being dividedfrom said hearth chamber by a constricted throat, burner means forforming in said hearth chamber a flame with a mobile fuel having atemperature of at least about 3000 F., the products of combustion ofwhich are reducing, said constricted throat serving to increase thevelocity of said products of combustion as they pass into said upperchamber, and means for feeding into said upper chamber a finely dividediron-bearing material.

10. The apparatus claimed in claim 9,-including means for feeding intosaid hearth chamber a reducing gas at a point remote from the origin ofsaid flame whereby to increase the velocity of the gases passing intosaid upper chamber.

11. Apparatus as claimed in claim 9, in combination with means forreceiving the products of combustion from said upper chamber and dryingand reheating them, reducing apparatus in which said dried and reheatedproducts of combustion are associated with finely divided iron ore andflux to effect at least a partial reduction of said iron ore and meansfor feeding the solid material so treated into said upper chamber ofsaid furnace.

12. In apparatus for the purpose described, a furnace for melting iron,said furnace having a sealed hearth chamber, burner means in said hearthchamber for producing a flame in said furnace, said flame havingreducing products of combustion, means ahead of said burner for crackingsaid mobile fuel in the presence of finely divided iron-bearing materialentrained therein prior to the ignition thereof to form said flame,means for associating said products of combustion with finely dividediron ore whereby to reduce said iron ore, and means for delivering thereduced'material into said hearth chamber so that said reduced materialis melted.

'13. The structure claimed in claim 12, wherein said furnace has anupper chamber through which said products of combustion pass and meansin said upper chamber for causing said products of combustion to act onfinely divided iron-bearing material suspended therein.

14. The structure claimed in claim 13, including means for associatingthe products of combustion after passing through said upper chamber withfinely divided iron ore in a reducing apparatus and means for deliveringthe reduced product to and entraining it in the said mobile fuel aheadof said cracking means.

15. In apparatus for the purpose described, a furnace having a sealedhearth chamber for melting iron, an upper chamber through which saidproducts of combustion pass, burner means for producing in said hearthchamber from a mobile fuel a reducing flame having a temperature of atleast about 3000 F., a heat exchanger in said upper chamber exposed tothe heat of said products of combustion, means for passing said mobilefuel through said heat exchanger ahead of said burner means, and meansfor entraining in said mobile fuel ahead of said heat exchanger a finelydivided, iron-bearing material.

References Cited in the file of this patent UNITED STATES PATENTS190,926 St. John May 15, 1877 1,490,012 Kapteyn Apr. 8, 1924 1,704,029Baily Mar. 5, 1929 1,775,713 Baily Sept. 16, 1930 1,948,697 BrassertFeb. 27, 1934 2,330,487 Grace Sept. 28, 1943 2,420,398 Kinney May 13,1947 2,503,555 Lykken Apr. 11, 1950 2,538,201 Kalbach Jan. 16, 19512,544,697 Lewis Mar. 13, 1951 2,547,685 Brassert et al Apr. 3, 1951FOREIGN PATENTS 370,636 Great Britain Apr. 14, 1932

1. IN A PROCESS OF REDUCING AND SMELTING IRON ORE INCLUDING THE STEPS OFPRODUCING IN A FURNACE WITH A MOBILE FUEL A FLAME HAVING A TEMPERATUREOF AT LEAST SUBSTANTIALLY 3000* F. THE PRODUCTS OF COMBUSTION OF WHICHARE REDUCING TO IRON OXIDE, EMPLOYING SAID REDUCING PRODUCTS OFCOMBUSTION IN HEATED CONDITION TO REDUCE FINELY DIVIDED IRON ORE TOIRON, AND MELTING SAID REDUCED IRON BY MEANS OF THE HEAT OF SAID FLAME,THE FURTHER STEPS OF CRACKING SAID MOBILE FUEL PRIOR TO IGNITION THEREOFTO PRODUCE SAID FLAME BY THE APPLICATION OF HEAT TO SAID MOBILE FUEL,AND HAVING PRESENT IN SAID FUEL AT THE TIME OF CRACKING A FINELY DIVIDEDMATERIAL WHICH IS INTRODUCED INTO SAID FURNACE THROUGH SAID FLAME.